SQLite

**   *  Definitions of sqlite3_io_methods objects for all locking
**      methods plus "finder" functions for each locking method.
**   *  sqlite3_vfs method implementations.
**   *  Locking primitives for the proxy uber-locking-method. (MacOSX only)
**   *  Definitions of sqlite3_vfs objects for all locking methods
**      plus implementations of sqlite3_os_init() and sqlite3_os_end().
**
** $Id: os_unix.c,v 1.243 2009/03/21 14:41:04 drh Exp $
*/
#include "sqliteInt.h"
#if SQLITE_OS_UNIX              /* This file is used on unix only */

/*
** There are various methods for file locking used for concurrency
** control:

** it work better.
**
** The SQLITE_NO_SYNC macro disables all fsync()s.  This is useful
** for testing when we want to run through the test suite quickly.
** You are strongly advised *not* to deploy with SQLITE_NO_SYNC
** enabled, however, since with SQLITE_NO_SYNC enabled, an OS crash
** or power failure will likely corrupt the database file.
**
** SQLite sets the dataOnly flag if the size of the file is unchanged.
** The idea behind dataOnly is that it should only write the file content
** to disk, not the inode.  We only set dataOnly if the file size is 
** unchanged since the file size is part of the inode.  However, 
** Ted Ts'o tells us that fdatasync() will also write the inode if the
** file size has changed.  The only real difference between fdatasync()
** and fsync(), Ted tells us, is that fdatasync() will not flush the
** inode if the mtime or owner or other inode attributes have changed.
** We only care about the file size, not the other file attributes, so
** as far as SQLite is concerned, an fdatasync() is always adequate.
** So, we always use fdatasync() if it is available, regardless of
** the value of the dataOnly flag.
*/
static int full_fsync(int fd, int fullSync, int dataOnly){
  int rc;

  /* The following "ifdef/elif/else/" block has the same structure as
  ** the one below. It is replicated here solely to avoid cluttering 
  ** up the real code with the UNUSED_PARAMETER() macros.
  */
#ifdef SQLITE_NO_SYNC
  UNUSED_PARAMETER(fd);
  UNUSED_PARAMETER(fullSync);
  UNUSED_PARAMETER(dataOnly);
#elif HAVE_FULLFSYNC
  UNUSED_PARAMETER(dataOnly);
#else
  UNUSED_PARAMETER(fullSync);
  UNUSED_PARAMETER(dataOnly);
#endif

  /* Record the number of times that we do a normal fsync() and 
  ** FULLSYNC.  This is used during testing to verify that this procedure
  ** gets called with the correct arguments.
  */
#ifdef SQLITE_TEST

  ** and (for now) ignore the overhead of a superfluous fcntl call.  
  ** It'd be better to detect fullfsync support once and avoid 
  ** the fcntl call every time sync is called.
  */
  if( rc ) rc = fsync(fd);

#else 

  rc = fdatasync(fd);
#if OS_VXWORKS
  if( rc==-1 && errno==ENOTSUP ){
    rc = fsync(fd);
  }
#endif /* OS_VXWORKS */



#endif /* ifdef SQLITE_NO_SYNC elif HAVE_FULLFSYNC */

  if( OS_VXWORKS && rc!= -1 ){
    rc = 0;
  }
  return rc;
}